1. Field of the Invention
The present invention relates to a fine processing method for forming patterns on semiconductors, metal or insulating materials and, more particularly, to a method and apparatus for fine processing without employing a resist.
2. Related Background Art
Photolithography is one of the important techniques for manufacturing semiconductor devices, in which the structure of a device is formed on a substrate by fine processing according to a desired pattern. Conventionally, this technique is performed by a rather complicated procedure including resist application, pattern exposure, development, etching, resist removal, etc.
Since, in the processes of resist application, development and resist removal solutions are used, photolithography cannot be performed in a completely dry condition. The resist peeled off the substrate may remain as dust and cause defects, in which case the yield decreases. Therefore, a film forming and etching step containing fine processing, rather than the wet process employing solutions, is mainly a dry process employing a plasma or an excited gas in a vacuum or a low-pressure gas atmosphere.
In the development of devices, such as semiconductor memory devices, of a larger capacity and a higher performance, the circuit patterns and structures thereof have become finer and more complex. Also, in the development of larger-size apparatuses, such as liquid crystal displays or plasma displays, the function of the devices employed therein have become complex. When the above-mentioned photolithography is employed to manufacture such devices, the procedure becomes even more complicated, pushing up production costs, and the number of defects caused by the residues of peeled resist increases, resulting in a lowered yield. Even when the dry process is employed instead of photolithography, the problems resulting from the peeled resist remain unsolved.
In the Lecture Manuscript of the 5th Dry Process Symposium, p.97 (1983), Sekine, Okano and Horiike describe a photoetching technique whose procedure for forming a pattern on a substrate is substantially simplified, compared with the complex process of photolithography employing the above mentioned resist.
FIGS. 12 and 13 schematically illustrate a photoetching apparatus described in the above paper, showing a material to be processed 101, a material supporting table 1202, a vacuum-tight etching chamber 1203, a garb inlet 1204, a light source (an Hg-Xe lamp of 200 W) 1205, a fused quartz lens 1206, a fused quartz window 1207, a light-shield box 1208 and a mask 1309 comprising a fused quartz substrate having an Al pattern thereon.
The photoetching method employing the above-described apparatus will be described. A material 101 is mounted on the material supporting table 1202, and the etching chamber 1203 is vacuum-evacuated to 10.sup.-4 torr or lower. Then, an etching gas is introduced through the gas inlet 1204 into the etching chamber 1203. The pressure in the etching chamber 1203 is set at a desired level in a range from 1 to 760 torr by adjusting a vacuum evacuation system. The Hg-Xe lamp 1205 is turned on to emit UV rays, which are converged by the fused quartz lens 1206 into a spot having a diameter of 2 mm on the surface of the material 101. The area irradiated by the UV rays is etched by the photochemical reaction between the irradiated area and the etching gas. A pattern is directly formed on the material 101 without requiring a resist, by employing the mask 1309 placed in the immediate front of the material 101, as shown in FIG. 13.
When the material 101 is a substrate having a deposited polycrystalline (poly-Si) film, chlorine is used as the etching gas. The above paper reports that normal etching is performed on a non-doped poly-Si at a speed of 80 .ANG./min or less, on a phosphorus-doped poly-Si (n.sup.+ -poly-Si) at 7000 .ANG./min or less, and on a boron-doped poly-Si (p.sup.+ -poly-Si) at 80 .ANG./min or less.
A case is reported in which patterning is performed as follows: a non-doped poly-Si is used as the material 101; the mask 1309 is placed at a distance of 100 .mu.m in front of the material 101, as shown in FIG. 13; and the material 101 is selectively irradiated for etching with UV rays coming through the mask 1309 in an atmosphere of chlorine, and thus only the irradiated areas are etched.
The method as described above provides a simple step without requiring resist application, development, resist removal, etc. Thus, this method increases the yield and substantially reduces costs. It also provides etching without damage, unlike the conventional reactive ion etching in which damage is caused by ion irradiation.
However, this photoetching method is unsuitable for high-precision fine processing requiring high fidelity to the pattern because light scatters or diffracts in the fine processing groove. If complete anisotropy etching is to be carried out, a film for protecting the side wall must be formed. Such a film is left as debris in the device after the etching process and gives a bad effect thereto.
As described above, the speed of etching on a non-doped poly-Si or a p.sup.+ -poly-Si is at fastest 80 .ANG./min. Such speed is two orders in magnitude smaller than that of plasma etching.
Although UV rays are converged into a spot having a diameter of 2 mm in the above conventional example, UV rays are converged, in real practice, to irradiate the entire surface of a Si substrate of 4 to 8 inches in size. Thus, the irradiation intensity of UV rays reduces to 4/10000 or less of the intensity in the above example. Because the etching speed substantially depends on the irradiation intensity, the speed accordingly becomes very slow.
In the above-described photolithography, there is a tendency that as the process thereof becomes complicated, more debris or trash remains in the device to cause increased defects in the devices and a reduced yield.
Therefore, there is a demand for a thin film pattern forming method which does not require a photoresist.